The present invention relates generally to an ATM (Asynchronous Transfer Mode) switching system and, more particularly, to an LSI-based line interface of an ATM switch, for inserting a management cell.
FIG. 6 is a diagram illustrating a construction of a line interface of a prior art ATM switch.
As shown in FIG. 6, a line interface 110 constructed of one LSI and provided between a physical layer 120 and an ATM cell switch 130. The line interface 110 includes an input cell processing portion 111, a first template 113, an output cell processing portion 112 and a second template 114. Herein, a cell flow from the physical layer 120 toward the ATM switch 130 is called a "input cell flow". A cell flow from the ATM switch 130 toward the physical layer 120 is termed an "output cell flow". The input cell processing portion 111 and the output cell processing portion 112 individually execute a normal ATM process and an insertion/divergence process etc with respect to the input cell flow and the output cell flow as well.
Generally, the ATM switching system requires such a function that network management cells such as an OAM (Operation And Maintenance) cell and an RM (Resource Management) cell etc are generated by a switch node and inserted into the cell flow. These inserted cells have a predetermined format and are therefore easy to generated on condition that they hold a cell data template.
The line interface 110 constituting the conventional ATM switch holds the cell template (format) through a RAM or a ROM within the LSI in order to correspond to the insertion of the cells such as the OAM cells and the RM cells having the fixed format. These are the first template 113 and the second template 114. Then, the input cell processing portion 111 and the output cell processing portion 112 execute the process of inserting the management cells into the input cell flow or the output cell flow on the basis of the first template 113 or the second template 114 as the necessity arises.
The line interface LSI constituting the prior art ATM switch, however, holds those templates through the RAM or the ROM within the LSI in order to correspond to the insertion of the cells such as the OAM cells and the RAM cells having the fixed format, which leads to an increase in size of the line interface LSI. Further, when using the ROM, the fixed format of the template is made unchangeable enough to produce such a possibility that the format might lose a degree of freedom to change corresponding to the system.
Moreover, when inserting the network management cells such as the OAM cells and the RM cells, in the conventional ATM switch, a fixed type sequencer executes a series of processes ranging from a judgement of a necessity for inserting the management cells, a generation of the management cells to the insertions into the input/output cell flows, and it was therefore impossible to flexibly deal with alterations in processing contents that correspond to the systems and alterations due to changes in specifications of communications protocol.
Further, a system for incorporating a microcode sequencer into the line interface LSI in the line interface module has been proposed as a system for coping with the problem concerning the flexibility described above. This system is, however, based on the premise that the series of processes ranging from the judgement of the necessity for inserting the management cells to the insertion into the cell flow are to be executed within a 1-cell processing time by two microcode sequencers for respectively managing the I/O cell flows. Therefore, an excessive performance has been demanded of a processing throughput of the sequencer.